Unreliable timing marks

[Adrian]

I ordered a piston stop as I think it’s a nice simple procedure......except.......it arrived yesterday and tried it just, it doesn’t stop. It was tightened all the way to the collar and I can turn the engine a full revolution. Are they different lengths?

 

This one seems to be longer

https://www.ebay.co.uk/itm/Husqvarna-TC50-Piston-Stop-10mm-and-14mm-spark-plugs-Quick-Dispatch/172969951655?epid=9003707153&hash=item2845d001a7:g:K7wAAOSwNnRYicX8

 

 

 

 

[dave.vitesse]

Adrian, I would say the extension of the piston stop is not long enough to engage the piston.   

There is an old method to find TDC, its by fixing a balloon to a drilled out spark plug. When the balloon reaches its full inflation point the piston is TDC. When it gets passed TDC the balloon with start to deflate. The valves also have to be sealing correctly.

You have to ensure both valves are closed either by adjusting the rockers wide or removing the rockers shaft. If you remove the rockers shaft then remove all spark plugs. A pipe from a compression tester could be used instead of the drilled out spark plug.

Dave

[Waynebaby]

Adrian,

Snap! I ordered the same thing and no, it isn't long enough. I think that they must come in a range of sizes!. I ended up checking TDC by using the depth probe end of a set of calipers but I still intend to get a piston stop of the right length because I'm sure it'll come in handy.

Wayne   

[Waynebaby]

Hi All,

I've spent a couple of hours fiddling about with the dizzy, two different strobe guns and a test lamp and I still can't see why my ignition needs to be so advanced for the engine to run sweetly.

I checked the orientation of the strobe pick up on the plug lead and get the same result whether or not it is clipped on with the "towards the plug" symbol facing towards or away from the plug, so the 25 degrees isn't a false reading introduced by operator error Pete.

I've cross checked the adjustable strobe gun with a simpler strobe lamp and get the same result showing it's not an anomalous reading caused by an incorrect scale on the advance adjuster knob.

I've set the ignition to 10 degrees statically with the rotor arm pointing at the #1 cylinder lead and confirmed the plug lead orientation in the cap is correct. Just to be sure I shuffled the leads to and fro as Colin suggested but the engine wouldn't start.

So I'm still non the wiser. If I set the ignition timing to the correct specification the engine runs badly, but if I set it up "by ear" if runs well and shows no indication of pre-ignition - it just so happens that the sweet spot is at 25 degrees of advance BTDC! For the time being I'm going to pretend I never checked the timing with the strobe gun and get on with enjoying driving my GT6, which for the first time since I got it actually feels like a sports car!

Wayne

[AidanT]

Good for you Wayne

Aidan 

[JohnD]

Wayne,

Have we discussed stuck centrifugal advance?

Get your strobe out again, warm up etc etc.    Watch the marks as you rev the engine.   It should advance as the revs rise, to a maximum of about 20 degrees more than the base setting.

If it doesn't move, the the centrifugal mechanism has seized.

John

[Pete Lewis]

Thinking  daft but ,    Was the vac capsule disconnected although that wouldnt add 15deg to the static.

May be a valve timing check is worth a ellimination.

Pete

 

[Waynebaby]

Hi John/Pete,

The mechanical advance works and the check was done with the vacuum advance removed so it's not that I'm afraid.

What would a valve timing check involve? Would it be as simple as making sure both valves were fully shut on cylinder 1 when at TDC?

Wayne

[Pete Lewis]

Get the 11 12 rockers in balance , ie one part down one part up

Set 1 and 2 to 0.040"

Then turn onnto align tdc marks 

The gap at 1 and 2 should be equal

Pete

[dougbgt6]

When Pete and I had that "unfortunate incident", going all the way to Guilford for someone who turned out not to be a member, Pete set the timing roughly by timing marks and it didn't go. It became apparent the leads were exactly as Colins above and once moved one post all around, deep joy, until Pete discovered the guy was a mountebank. 

I vaguely recall our beloved GT6 registrar,  Andy Cook, went to the IoW  weekend, his GT broke down and he found his timing was WAY out. He discovered his timing chain had eaten a few teeth on the cam gear and jumped half way round. Bearing that in mind I wonder if it's worth taking the timing cover off and eyeballing the chain and gears?

Doug

[daverclasper]

That hole in bell housing sounds a good idea Pete. I wish those design yobs at the factory had thought of it!.

A question or two please.

Is the engine side of pulley locked to the crank, if so, therefore timing won't alter?, (if not would timing advance or retard).

If only the outer ring moves/slips, then would the marks be showing advance, or retard? .

Cheers, Dave

     

Edited April 24, 2018 by daverclasper

[Gully]

Remember working on a car when I was at Poly and checking the timing marks on the flywheel which were visible when a small cover plate was removed - blowed if I can recall what the vehicle was, but it was a sensible arrangement!

Gully

[Waynebaby]

Thanks for that suggestion Pete.

I need to take the rocker box off to sort out a noisy tappet so I'll check the valve timing at the same time using your technique. I won't get around to it for a few days but I'll let you know what I find.

Wayne 

[Pete Lewis]

It probly wont prove much but at least you will know its pretty much ok

fit a temporary vac gauge , what sort of reading do you get

you need around 18to 20 ins hg at idle    if you have over advanced it may be up in the 22 to 24    is toooo high..

Pete

[JohnD]

12 hours ago, daverclasper said:

Is the engine side of pulley locked to the crank, if so, therefore timing won't alter?, (if not would timing advance or retard).

If only the outer ring moves/slips, then would the marks be showing advance, or retard? .

Cheers, Dave     

The crank has a Woodruff key that engages with the pulley.

As I think I said above, if the outer ring slips, it could be out a little bit, either way, making timing difficult, or a whole lot, making it impossible.

Kas Kastner knew about this possibility.  he would drill down through the V of a new pulley, into the hub, so that a split pin would pass full depth.   Thereafter, if the pin would not pass, the  the pulley had moved.    Bit late for most of us.

John

[Mad4classics]

The distributor advance at any rpm is the sum of static + mechanical + vacuum.

Very generally a total advance of ~ 32-33 degrees all-in is about right.

So is the distributor the correct one? Is the vacuum advance the correct one (mine wasn't)?

Also a worn distributor will give misleading figures. The springs could have weakened or the distributor worn so that you're getting more advance at tickover than you should.

With a badly worn distributor you can get far less than 30+ degrees all-in by adhearing to the book figures because you've started with more advance than you bargined for.

(All figures here rough guide only)

Gully,

Early Mini engines had a plate on the bell housing you could rotate aside by slackening a bolt in order to view timing marks on the flywheel. Probably others too...

[Adrian]

Just to finish the TDC stuff - success! I bought a longer piston stop from Bikers Tool box - arrived the following day.

 

I could actually see the top of the domed piston at the top of the throw when shining a torch in cylinder 1. Word of caution to anyone using this - its too long to allow you to complete a full cycle, the valves actually foul against it. So if using it on the compression check the valves are clear via the spark plug hole before  inserting,  hand tight and rotate crank for the first mark. Remove when done and complete rotation until the piston starts to drops, then reinsert and back up the piston to contact the stop. Done!!! Gives me greater confidence after changing the timing wheel/chain.

 

Thanks  

 

 

 

[Pete Lewis]

Warning do make sure you remove it before you try to crank it on the starter

You know...... when enthusiasm overtakes sensible.

Pete

 

[JohnD]

 I'm amazed, and bit concerned that you fouled the valves.  You must have been doing the test, NOT at TDC on the firing stroke, but between cycles on the overlap.

At TDC on the firing stroke, both valves are and remain firmly closed, right across the top of the stroke, giving you plenty of room to turn the crank both ways from TDC.  This makes doing the test so much simpler, repeatable and less faff.  

Look at the dizzy to see if you are on the firing stroke,  The rotor arm should be pointing to No.1.

JOhn

[Pete Lewis]

 I'll Echo  John on that one 

 

[dave.vitesse]

John's spot on.

Dave

[Waynebaby]

On 24/04/2018 at 5:39 PM, Pete Lewis said:

Get the 11 12 rockers in balance , ie one part down one part up

Set 1 and 2 to 0.040"

Then turn onnto align tdc marks 

The gap at 1 and 2 should be equal

Pete

Hi All,

I followed Uncle Pete's advice and have spent an hour or so in the garage playing with a dial gauge and a 0.040" feeler gauge. I'm very relieved to report that whatever it is that is causing my engine to seemingly prefer such a high degree of static ignition advance, it hasn't anything to do with the cam-shaft being out of time with the crankshaft. Set up as Pete suggests, the gaps at valves 1 and 2 were within a 001" of each other at TDC, which is equal in my book. I have to confess that Doug's story of a timing chain chewing up the cam wheel had me worried. I have noted however that the official workshop manual recommends changing the timing chain every 30,000 miles and since mines probably done almost twice that I've got something new to add to next winters list of jobs.

I think I've almost run out of possible causes of the weird ignition advance figures but will try looking at the vacuum level as Pete suggests to get another line of evidence (I just need to find a vacuum gauge) Picking up on the comment from Mad4Classics, I am starting to wonder if a dizzy rebuild/replacement is on the cards. I'd be more keen on spending money on getting to the bottom of the odd figures if it wasn't for the fact that the car is running better than it ever has before under my ownership! 

Wayne

[Pete Lewis]

maybe now is the time to have a cuppa and enjoy the drive  !!!!

pleased the cam timing worked out correct ...  its not hard to get a check completed without anything special

Pete

[Mad4classics]

Wayne,

I was coming from the point of view of the timing mark probably being OK.

The distributor however gets a hard life and is often overlooked when it comes to rebuild time.  However the springs do weaken over time and they wear the posts on which they attach. The weights also wear their pivot posts and the main shaft bushes wear etc...

Sometimes the effect of all this is that the distributor has an initial advance even at tickover / static and as the maximum mechanical advance is limited (22deg for a MK3 GT6;20deg MK2 and 15/19degree MK1 according to my book) then the effective all-in advance will not be as much if you stick by the book figure. But you can compensate for this by advancing the ignition timing, this puts it about right in the mid RPM range which is where the engine spends most time when your driving - but it will be over advanced low down where you probably won't notice a problem and under advanced as you approach the RED line (we don't do that any more ) .

It was just my musings when you described advancing the ignition meant a whole better driving experience.

Now as Pete says it's definitely time for a cup of tea.

David

 

[Adrian]

I'm a bit confused and concerned now, showing my inexperience and apologies as there are two threads running here. if the cylinder is on the compression stroke both valves should be closed and can be simply tested by pressure build up if the finger is over the plug hole. They are and it is when at TDC (able to get a feeler gauge in). Also dist lines up with No 1 (ish as new dist so will need fine tuning).

 

Perhaps I described it wrong, as the manuals say don't reverse the engine rotation so wanted to get front - then back which meant cycling through the valve cycle. Didn't work due to valves so,

1. did up cycle (stopped at 6cm before TDC)  then I took the piston stop out,

2.  rotated past TDC, re-inserted piston stop, 

3. I did reverse slightly till it stopped again, unsurprisingly 6cm past TDC.

I think its right unless I'm missing a T-shirt moment!

 

Adrian